QLowEnergyController - service discovery (OS X, iOS)

Implement discoverServices and delegate's methods to work with a service
discovery on a peripheral.
- CBUUID (it's internal data) can be only 2 bytes long (16-bit shortened UUID)
  despite of the docs saying 'CBUUID is a 16-bit UUID'.
- property 'isPrimary' did not exist prior to 10.9 SDK (OS X).

Change-Id: If692d147c0479ed69a331514617e3ef2a986cdf4
Reviewed-by: Alex Blasche <alexander.blasche@theqtcompany.com>